The present invention relates to compositions that result in enhanced osteogenesis across a broad range of bony repair indications and methods of using the compositions in a delivery vehicle for improved repair of bony lesions.
The U.S. published application 2005/0196425 to Zamora et al. entitled. “Positive modulator of BMP-2” teaches a compound comprising a bone morphogenic protein-2 (BMP-2) analogue which is useful to repair bone lesions and a method in which the compound can augment endogenous or exogenously added BMP-2 activity. It further teaches that there are a number of commercially available bone graft substitutes that are osteoconductive that the BMP-2 modulator compounds could modify. The osteoconductive materials included a number of calcium phosphate containing composites. The compound is an additive to bone matrix or bone graft materials or controlled or associated with drug delivery devices among others. US 2005/0196425, however, does not disclose peptide and osteoconductive formulations that permit efficient peptide binding to osteoconductive materials, controlled differential release through manipulating the osteoconductive composition, manipulating the peptide composition, concentration of the compound attached thereto, and/or manipulating the calcium sulfate concentration. For this application, the positive modulator of BMP-2 will be referred to as the co-activator/amplifier.
Osteoconduction can be described as the process of forming bone on a graft material that is placed into a void in a bony environment. Broadly speaking osteoconduction means that bone grows on a surface. Osteoconduction requires a scaffold for cells to move into the graft site and produce bone. Scaffold materials can be categorized into four types: allograft bone, natural polymers (hyaluronates, fibrin, carboxymethyl cellulose, chitosan, collagen, etc.), synthetic polymers (polylactic acid (PLA), polyglycolic acid (PGA)), and inorganic materials (e.g. hydroxyapatite (HA), tricalcium phosphate (TCP), calcium sulfate (CaS)). A number of synthetic osteoconductive bone graft materials have been developed for purposes of filling boney voids. These graft materials, however, are only osteoconductive and provide a scaffold for viable bone healing, including ingrowth of neovasculature and the infiltration of osteogenic precursor cells into the graft site.
Osteoinduction is the process by which osteogenesis is induced and is a process regularly seen in any type of bone healing. Osteoinduction implies the recruitment of immature cells and the stimulation of these cells to develop into preosteoblasts. In a bone healing environment, the majority of bone healing is dependent on osteoinduction. This process is typically associated with the presence of bone growth factors (principally bone morphogenic proteins) within the bone healing environment.
Osteoinduction can be influenced by a number of proteins or growth factors, growth or new blood vessels (angiogenesis). These proteins cause healing bone to vascularize, mineralize, and function mechanically. They can induce mesenchymal-derived cells to differentiate into bone cells. The proteins that enhance bone healing include the bone morphogenetic proteins, insulin-like growth factors, transforming growth factors, platelet derived growth factor, and fibroblast growth factor among others. The most well-known of these proteins are the BMPs which induce mesenchymal cells to differentiate into bone cells. Other proteins influence bone healing in different ways. Transforming growth factor and fibroblast growth factor regulate angiogenesis and can influence bone formation and extracellular matrix synthesis. Extracellular matrix molecules such as osteonectin, fibronectin, osteonectin, laminin, and osteocalcin promote cell activation, cell attachment and facilitate cell migration.
While any healing bone lesion is an osteoinductive environment, not all osteoinductive environments (bone lesions) have the ability to undergo a full or complete healing. This has led to the use of recombinant bone morphogenic proteins to induce osteoinduction in graft materials thereby to induce stem cells to differentiate into mature bone cells.
U.S. Pat. No. 7,041,641 to Rueger et al. demonstrates any number of bone morphogenic proteins (BMPs) and growth factors combined with a number of scaffolds (including HA and TCP) and a binder for bone repair. These graft materials are, however, expensive and can lead to exuberant or ectopic bone production.
U.S. Pat. No. 6,949,251 Dalal et al. discloses a beta Tricalcium Phosphate (β-TCP) particle with any number of BMPs and/or a binder (CMC, Hyaluronate, etc.) for bone repair.
U.S. Pat. No. 6,426,332 Rueger et al. discloses 0TCP as an osteoconductive material with any number of bioactive agents combined therewith, for example BMP-2. The bioactive agent is dispersed in a biocompatible, non-rigid amorphous carrier having no defined surfaces, wherein said carrier is selected from the group consisting of poloxamers; gelatins; polyethylene glycols (PEG); dextrans; and vegetable oils.
A commercially available product for periodontal bone repair, GEM-21S™, utilizes a β-TCP granule coated with platelet derived growth factor “PDGF.” Saito et al. (JBMR 77A:700-6 (2006)) utilized the 73-92 peptide derived from 73-92 of the BMP-2 knuckle epitope. This peptide was coated on aTCP (OCTCP) cylinders and implanted in 20 mm long defects. Konishi et al. (J. Spine Disorders & Tech.) and Minamide et al. (Spine 2001 26(8):933-9) demonstrated BMP combined with hydroxyapatite granules for lumbar fusion.
Delivery of small molecules (such as peptides) for therapeutic indications is usually accomplished by various encapsulation technologies—microspheres, for example, in which the molecule is encapsulated in a vesicle which degrades over time to release the peptide. Delivery of a small molecule from the surface of a medical device has been challenging as small molecules rarely have physical properties that provide sufficient binding properties to a biomaterial surface. Often, the peptide is covalently attached to the surface in an effort to prevent rapid release (Saito et al., J. Biomed Mater Res 70A:115-121 (2004; Seol Y-J et al., J. Biomed. Mater Res (A) (2006)) (Varkey et al., Expert Opin. Drug Deliv. 2004 November; 1(1):19-36. Growth factor delivery for bone repair, Varkey et al.). One drawback of covalent crosslinks is the molecule is unable to release and influence the surrounding osteoconductive environment.
The delivery kinetics and quantities of a synthetic compound comprising a BMP-2 amplifier/co-activator may be specifically tailored to the indication of choice. It should be recognized that after a bony lesion is made, there is a reparative response that results in the cellular production of BMP-2, and furthermore, that this production occurs over a given time sequence with an upregulation period eventually followed by downregulation. Niikura et al. (2006 ORS, #1673) measured BMP-2 production over time in standard fractures and non-unions in rats and demonstrated less BMP-2 production in non-unions than in standard fractures and increasing amounts of BMP-2 up to 21 days followed by a decline in expression at 28 days. BMP-2 expression has been detected in the human fracture callus (Kloen et al., 2003, 362-371). Furthermore, Murnaghan et al. (JOR 2005, 23:625-631) demonstrated in a mouse fracture trial that BMP-2 administered to the fracture at day 0 or 4 produced greater repair than that introduced at day 8. It should be noted that in this case BMP-2 is timed with the production of stem cells that can be differentiated to bone and is not timed with endogenous BMP-2 production.
A synthetic growth factor identified as B2A2-K-NS was first disclosed by Zamora et al. in U.S. patent application titled Positive Modulator of Bone Morphogenic Protein-2 having Ser. No. 11/064,039 filed Feb. 22, 2005 in addition to disclosing various other peptides. However, it was not disclosed to combine the synthetic growth factor with an osteoconductive material as a composition for treating bone lesions.
There is, therefore, a need for a composition which can act as a bone void filler material and which is comprised of a synthetic growth factor analogue which can act as an amplifier/co-activator of osteoinduction, and which can attached to and released from an osteoconductive material to enhance boney repair and healing processes.
There are also number of surgical procedures in orthopedics wherein augmentation of bone repair would be particularly beneficial including fusion procedures including those of the spine and ankle; in filling the voids in bones resultant from traumatic injury; in the treatment of non-unions; fracture healing in all skeletal elements; in fixation of internal hardware such as rods, plates, screws, and the like; in concert with spinal cages or vertebral body replacements; and in the augmentation of implanted wedges, pedicle screws, or rings. These types of procedures and the associated hardware would be known to those skilled in the art.